Spreader action in concrete form ties is important and is required in order to keep both adjacent forms a specified distance apart during the concrete pour and also to assure integrity of design, uniform thickness and planar surfaces of the poured concrete wall. In addition, during the pour the upper part of the forms has a tendency to close and reduce wall dimensions at the top, because of the relatively heavy pressures of the poured concrete at the bottom. Thus, the spreader action of ties has to overcome this problem.
The normally employed spreader systems of conventional ties depend heavily on the rigidity of tie rods themselves. These rods have at each end projected swedging or similar provisions to support and maintain washers or cones inside of forms exactly at the face of the contemplated concrete wall. Consequently, washers or cones, larger than holes in the plywood, engage the inner face of the plywood and usually other members are designed to transfer compressive forces of exterior tie holding devices to the tie rods. Ties of this type require stripping of forms first and then removal of cones or perhaps break of the tie ends with washers after the forms are removed.
In the case of the commonly known pull-out-ties and tapered ties the rods are inserted through both erected forms, through the holes in the plywood of minimum required size to both permit entry of the rods and prevents excessive leakage of concrete grout. After concrete pour, the ties are removed before stripping of the forms. This procedure in closing and stripping forms is very beneficial and results in substantial labor savings in forming operations. It is also extremely conducive to the relatively new and economical large panel or gang forming operations normally handled by cranes. It is preferred, however, that the employed ties not have any built-in internal spreader system utilizing either projected washers or cones, which otherwise would be difficult if not impossible to insert through both forms in place, or to remove them from the concrete.
Some of the commercially available ties have notches on the external part of tie rods for special brackets engageable with outer form members (walers). However, an external spreader system of this type is not fully effective and practical, because it consists of many loose parts and is rather time consuming in execution. In addition, effective adjustment is limited to an inward direction only. If the forms are initially placed closer than the required distance or part of a form is leaning inwardly, existing exterior spreader systems simply cannot be used. These forms would then have to be reset or pulled out by hand, involving more work and costly crane time. There are a number of concrete construction personnel that still depend on the old fashioned deployment of pieces of wood between forms to be gradually removed as pour of concrete progresses.
To date, a fully effective, practical and economical spreader system is not in existence for the above group of ties with threaded ends which are inserted through both forms while in place, and after the ties are removed from the concrete both forms are free for stripping.
These ties with threaded ends are advantageous because they are the fastest and the most economical for gang forming. Also, completely removable ties of this type eliminate any possibility of rust marks. They are used more and more, especially with the growing volume of architectural concrete where it would be more convenient for better patching and matching of the concrete color and texture.